A high voltage DC power supply system is required for driving an electric machine that incorporates a high voltage (HV) electrical drive motor and electric auxiliaries. The integrity of the high voltage system is critical to the reliability and safety of the machine. Typically, the machine frame will be electrically isolated from the terminals or conductors of the high voltage power supply.
Under normal conditions, leakage currents on the order of microamps exist between the conductors of the high voltage power supply and the machine frame. Thus, the leakage resistances between the conductors of the high voltage power supply and the frame are normally very high. However, electric current from a high voltage power supply may leak to a machine frame. Such leakage currents, when significant, may be an indication of machine component fatigue or failure of a conductor's insulation. In order to ensure the proper operating conditions and the safety of the machines, it is necessary to detect electrical leakage between the conductors of the high voltage power supply and the machine frame.
Conventional systems and methods have been implemented to detect electrical leakage. For example, U.S. Pat. No. 6,700,384 to Yugou discloses a power source device having a cell unit comprising a plurality of cells. In Yugou, a first current line having two voltage dividing resistors interposed therebetween is connected between a positive side terminal and a negative side terminal of the cell unit. A second current line having two protection resistors and two detection resistors interposed therebetween is also connected between a positive side terminal and a negative side terminal of the cell unit. An intermediate point of the second line is grounded via an insulation resistor. The voltage difference between a voltage (V1, V2) detected by the detection resistors and a reference voltage (Vc) obtained from a point of connection between the voltage dividing resistors is provided as the input to two Op-Amps serving as the input voltage (V1IN, V2IN). Based on the output voltage (V1OUT, V2OUT) obtained from the Op-Amps, leakage occurrence is detected.
While prior art systems may be effective to some extent for detecting electrical leakage, they do not address detecting electrical leakage in a balanced fault condition. The disclosed embodiments improve upon prior art systems by providing a leakage detection mechanism that detects electrical leakage in a circuit with balanced leakage resistance.